Image from Steve Bowers

There are many ways a space habitat can be provided with interior lighting; Bernal spheres, O'Neill cylinders and Stanford tori typically use mirrors and windows to bring sunlight in from the outside while Bishop rings and McKendree cylinders will often use central illuminators or luminaires, located on their axis. An alternative method is to decentralize the lighting system. The aforementioned McKendree cylinders for example are often built with multiple levels and only the innermost level could possibly receive light from an axis mounted light source. To provide lighting for each additional level illuminators have to be placed between the levels. This usually means the lights for one level are mounted on the underside of the level above it, its ceiling. Other examples are the Eder worlds, where the living space is under a thick capping layer, and the supramundane shells, which may enclose their star system's primary energy source, the sun itself. These alternate lighting systems don't have to be in any way complex and can be as simple as a series of flood lamps placed on top of towers all around the landscape. However the focus of the discussion is a type of mobile, free-flying illuminator called a suncloud. Actually sunclouds are a class of lighting systems; there are many different types of sunclouds as there are many different technologies that can be applied to create one. Sunclouds can be passive or active, single function or multipurpose, dumb matter or sentient.

One of the simplest suncloud types is little more than a large mass of aerogel, aka frozen smoke. With the internal voids filled with a lighter-than-air gas an aerogel suncloud can remain airborne for months at a time. The aerogel may lose some of its gas over this time but when it is manufactured it is usually also given a quantity of water as ballast, which it sheds as rain over the same period. In such a system concealed light projectors illuminate the sunclouds from below and it is the reflected light that illuminates the habitat's landscape. Given irregular shapes and set to tumble in flight these aerogel sunclouds appear to change shape just as real clouds do because the angle of view is always changing for anyone who cares to watch, and as a habitat will typically have a swarm of aerogel sunclouds in its lighting system it is unlikely a viewer will see the same cloud for a day or more. In larger habitats there may also be an additional effect concealing the artificial nature of these sunclouds - real clouds. At the opposite end of the range a suncloud can be an environmental vec.

Adumbrans are well suited for work as sunclouds, although the intelligence of an Adumbran is not necessarily needed for this job alone. In this utility fog suncloud the extra energy needed for its illumination duties also comes from a remote location. When a habitat uses this type of suncloud it typically has a number of low-powered masers hidden throughout its interior as a broadcast-power system. A suncloud will receive a maser beam and convert it into electrical energy, energy its foglets will use to emit light during the daytime hours or collect water vapour during the night time hours for periodic rain events. On the other-hand, sunclouds made of foglets can also actively fly to a recharging station as their storage cells become depleted. However storage capacity is limited so such recharging stations are typically placed near the sunclouds' normal operational area, and at altitude. For this reason habitats with end caps, sidewalls and rims close at hand (such as Bernal spheres, short O'Neill cylinders, Stanford tori and Bishop rings) are the best location for sunclouds which use recharging stations, while broadcast-power is the favoured system in longer habitats where end caps are too remote for quick and frequent recharging.

Of course it is not necessary for power to be supplied in this way. In larger habitats the sunclouds can also be larger and larger sunclouds can enclose buoyancy aids that may give it enough extra lift that they can carry their own power source. Again, one of the simplest sunclouds of this type is the aerogel mass. By fitting a suncloud of this type with large hydrogen filled voids and lightweight fuel cells it can burn-off the hydrogen during the day to provide light and rainwater but must land each night to get a refill of hydrogen. A large habitat with such a simple system has to employ a workforce of refuelers to hunt these clouds down, a job that requires long hours of working in the dark. This is often a difficult and unrewarding duty but higher tech levels are needed for a system with a longer-term power supply. However in particularly small habitats (Bernal spheres, small O'Neill cylinders and Stanford tori) an even simpler type of suncloud can be used. In such habitats, where the distance to the axis or some kind of overhead structure are very short, the sunclouds can be heavier than air and tethered from above. Moved about on an overhead track or gantry/crane system and powered through their tethers they require very little to maintain.

It is also not necessary for the lighting effects of these illuminators to be direct. While the visual impact of softly glowing clouds has proven to be acceptable to most bionts of terragen origin some have found it unsettling. However, if the habitat has a roof of some kind, backlighting can be provided. Stanford tori, multilevel McKendree cylinders, worldroofed moons, Eders and airwalled Ribbonworlds all have a ceiling over at least part of their living spaces and a suncloud can project its light upwards and on to this structure. This creates a visual effect that's closer to what is found on an open planetary surface.

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Development Notes
Text by AI Vin
Initially published on 12 July 2007.